1. Technical Field
The present invention relates to high-voltage semiconductor devices, and more particularly to improvements to termination structures associated with central active areas of high-voltage semiconductor devices.
2. Discussion of Related Art
In order to block high voltages, high voltage semiconductor devices are constructed on lightly doped semiconductor starting material. Due to the field effect, lightly doped p-type surfaces are particularly prone to depletion and inversion from positive charges abundantly present in dielectric films placed in contact with the surface to protect it from scratches or other mechanical damage. Regardless of the source of these positive charges, the field effect alters the effective spacing of the termination structure and degrades its ability to sustain voltage.
U.S. Pat. No. 5,345,101 describes guard ring termination structures for high voltage active devices. The structures have two regions of differing conductivity levels and depths but of the same conductivity type.
U.K. Patent Application No. GB2355110A and European Patent Application No. EP 1076363A3 describe edge portions of high voltage semiconductor device active areas with first regions of a first conductivity type, second and third regions of second and third conductivity types, and oxide layers.
T. TRAJKOVIC, F. UDREA, P. R. WAIND, & G. A. J. AMARATUNGA, THE EFFECT OF STATIC AND DYNAMIC PARASITIC CHARGE IN THE TERMINATION AREA OF HIGH VOLTAGE DEVICES AND POSSIBLE SOLUTIONS (2000) describes a termination structure having p+ floating rings with shallow, lightly doped p and n rings to either side of the p+ floating rings, and an oxide layer.
European Patent Application No. EP1076364A3 describes a voltage termination structure of a semiconductor device having a substrate of a first semiconductor type and having first and second regions of a second semiconductor type formed within the substrate region.
U.K. Patent Application No. GB2373094A describes a high voltage device surrounded by highly doped floating rings, the surface area between each pair of rings having an alternating pattern of lowly doped p and n type regions, and the device and rings being covered with a passivation layer.